Helicobacter pylori has emerged as one the world s most common infections and a major cause of morbidity, but little is known about the health impact of acute infection. The PI postulates that the temporary gastric hypoacidity that accompanies acute H.pylori infection increases the risk of diarrheal illness and failure to thrive in newly infected children. As initial test of this hypothesis, the PI will analyze previously collected data from a community cohort study of children in Lima, Peru. In order to confirm that gastric hypoacidity is the causal mechanism linking H.pylori infection to diarrheal disease, a novel assay-the quininium resin test--will be adapted and validated for use in children. This test will become a key component of a prospective cohort study designed to demonstrate that acute H.pylori infection leads to concurrent gastric achlorhydria and increased rates of diarrheal disease. This work will increase appreciation of the disease burden mused by H.pylori and could hasten development of an effective vaccine. It should also help to define the clinical syndrome of acute H.pylori infection. Specific aims of this project are: 1. To modify and validate assays for H.pylori infection for use in children, including serum IgG and IgM tests and a stool fecal antigen test. 2. To modify and validate the quininium exchange resin test for gastric hypochlorhydria. 3. To apply these assays in field studies to detect acute H.pylori infection and to determine the prevalence of gastric hypochlorhydria among acutely infected children. 4. To determine whether acute H.pylori infection is accompanied by gastrointestinal symptoms and to determine whether H.pylori infection leads to growth retardation or increases in diarrheal illness. The PI is a clinician and researcher with a career interest in the epidemiology of poorly understood infectious diseases. The PI's Immediate goal is to develop into a independent investigator specializing in translating laboratory diagnostics for use in fieldwork and in characterizing disease mechanisms that underlie the epidemiology of emerging pathogens. The PI's background in international health and epidemiology are ideally suited to conducting the proposed research plan and demonstrate a commitment to academic medicine. The career development plan detailed in this proposal solidifies the PI's prior training experiences while helping him to obtain rigorous training in conducting field trials and in developing expertise in the use of patient-oriented research to adapt diagnostic techniques for widespread use.